The print issue of the third layer sounds like one of a few different types of issues:
1) heat creep due to either issues with cooling or not extruding fast enough
2) Over retraction as mentioned above, causing a cooling blockage
3) To high of heat for the filament used. Have you done a test tower for the filament you are using?
I Had only minor issues with printing my parts in PETG and have modified the parts to reflect those changes. They are at this location with attributes of being remixes: https://www.thingiverse.com/thing:4102435
Hope folks find them useful. I changed out holes to better fit nuts and also added helical gear teeth for better transfer of power and smoother motion. There are other changes as well and as I said I hope that it helps folks. Anyone who needs prints done in the UK for now let me know.